INTERPRETATION
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Regional and Mesoscale Meteorology Team Cooperative Institute for Research in the Atmosphere (CIRA) Colorado State University Fort Collins, Colorado |
May 24, 1999
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Loop 1 GOES 10.7 µm imagery |
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The topic of this satellite discussion is gravity waves moving upstream from a large convective system in TX. On 12 May 1999 nocturnal convection formed in south-central TX. GOES 10.7 µm imagery between the hours of 0700 UTC and 1200 UTC indicate minimum cloud top temperatures of -74 C and an average cloud shield brightness temperature of -65 C (Loop 1). (Click on images to start loops) | xxx | 
GOES 6.7 µm imagery |
| Analysis of the GOES 6.7
µm channel (i.e., water vapor channel) displayed concentric waves
of warming and cooling brightness temperatures migrating upstream (to the
west) from the convective system in TX (Loop 2).
It is unlikely that mass transport of water vapor to the west can explain the phenomenon since the mean flow at anvil height is westerly. We conclude that the cooling is a result of vertical motion induced by gravity waves. The cooling rate is approximately 1.6 C per hour. Using 10 C per km as an approximate lapse rate near 300 mb, we calculate that the approximate vertical motion created by the gravity wave was 4 cm/s. The waves shown here appear to be gravity waves of the type discussed in Fovell et al. (1992), Pandya and Durran (1996), and Nachamkin (1998). Nachamkin’s research suggests that gravity wave responses from mesoscale convective systems (MCSs) are focused in the direction of the heat source tilt; i.e., the tilt of the latent heat released within the updraft. With this information, we hypothesize that the updrafts within the convective system in TX were tilted toward the west.
References Fovell, R., D.R. Durran, and J.R. Holton, 1992: Numerical simulations of convectively generated stratospheric gravity waves. J. Atmos. Sci., 49, 1427-1442. Nachamkin, J.E, 1998: Observational and numerical analysis of the genesis of a mesoscale convective system. Colorado State University Dissertation. Atmospheric Science Paper No. 643. Pandya, R.D. and D. Durran, 1996: The influence of convectively generated thermal forcing on the mesoscale circulation around squall lines. J. Atmos. Sci., 53, 2925-2951. |